Oracle and DB2 are the only RDBMS products that can auto-materialize views for you, but you can rig them yourself in PostgreSQL or anything that gives you a powerful enough trigger + procedural language. (And if performance is crucial, you'll end up hand-optimizing them in Oracle/DB2 as well. At least, back when I used Oracle in the 8.1 days.)
But while looking for examples of a certain PL/PGSQL feature this morning, I found Jonathan Gardner's materialized views page (link may be down; see the archive.org copy) which covers the subject so well that now I don't have anything left to add. Nicely done!
Incidently, this is just one more reason real procedural languages in the database are critical for most substantial projects. Implementing materialized views in your application logic would be worse than a joke.